Metal filament



May 10, 1927.

T. E. FOULKE METAL FILAMENT Filed July 29. 1922 TDI .2

` INSZENIDH.: TED' E. Tuul/KE,

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Patented May 10, 19227.

UNITED STATES PATENT OFFICE.

TED E. FOULKE, F CLEVELAND, OHIO, ASSIGNOB-TO GENERAL ELECTRIC COMPANY,

.A CORPORATION OF NEW YORK.

'METAL FILAMENT.

Application :tiled July 29, 1922. Serial No. 578,474.

My invention relates to metallic filament electric incandescent lampsand other electrical devices comprising filaments and more particularly to such lamps and devices in o which chemicals are employed to improve the vacuum or to prevent discoloration of the lamp during use, suoli chemicals being known as getters. The object of my inp vention is to improve such lamps and deio vices by reducing the shrinlrage due to breakage of the filaments, particularly during shipment of the lam s or devices. kMy

invention is particular y applicable to tungsten filaments containing thoria or other non-metalic material for preventing odsetting, since such filaments seem to be more injuriously aected by the getter than other filaments.

According to my invention the tungsten or other metallic filament is given a thin coating of metallic oxide, which ispreferably an oxide produced by oxidizing the surface of the lament wire itself. This coating is applied before the lamp is subjected to the preliminary or so-called. fiash aging, and, in fact, it is most conveniently done before the mounting of the filament in the lamp. One of the most effective methods of gettering lamps is disclosed in Patent No. 1,284,648, issued November 12, ,1918, to Fi'ederickW. Gill, and assigned to the assignee of the present application. .That method is to pass the filamentary wire through a suspension or solution of the gettering substance with such a speed of movement and with such a concentration of substance as to give the wire a coating of the proper amount. For example, the wire is run in a groove of a wheel which dips into a reservoir containing the suspension solution with which the wire is to be coated. Afterwards the coated wire is passed through a mixture of collodionwhich forms a thin covering ofcollodion on the film of getter. In this case, according to my invention, the oxide coating is applied to the lamentary wire before the application of the getter. l

It is customary to treat lamentary wire by the process disclosed in Pacz Patent 1,280,825, for the purpose of cleaning and otherwise putting the wire in condition for use as filaments. That process comprises a preliminary oxidation followed by reduction. I prefer to apply this process to the wire prior to the application of my process thereto.

In the drawing, Fig. 1 shows diagrammatically a side elevation of an apparatus by means of which my process may be carried out; and Fig. 2 shows a side elevation partly in section of a modification of the oxide coating portion of the apparatus.

Referring to the drawing, the tungsten or other wire 10, is carried on a reel 11, and passes continuously from this reel to the reel 12, which is power driven. The wire first passes through an electric heating device 13, which may be simply an alundum or other refractory tube Wound with the usual heating device resistance wire 14, which is connected to a suitable source of electrical energy. The temperature should be between The speed at which the wire is run should be such that it takes about .002 minutes for a point on the wire to pass from the entrance to the exit end of the tube. The wire next passes over the grooved wheel 15 and is carried down into the getter solution 16, which may be any suitable chemical held in solution or suspension and preferably such as is disclosed in the Gill application hereinbefore referred to. The wire then passes over the grooved wheel 17 and is guided through a collodion solution container in the receptacle 18, after which it passes over a drying unit 19, which is preferably lof the electrical resistance type.

In'. Fig. 2 is shown a modification of the oxide coating portion of' the apparatus. This comprises a pair of mercury contacts 20 and 21 through which the Wire passes. Theelectrical connections are such that a current passes through that portion of the wire which is between the contacts. The contact distance is so adjusted that the wire is hot for a period of .002 minutes. Some variation is permissible but it preferably should be less than plus or minus .0005 minutes This time can be obtained with the contacts set at a considerable distance with the wire traveling at high velocity, for instance, a distance of 31 centimeters and a speed of 75 meters per minute. or by putting the contact-s inuch closer together and running 'at a low velocity, for instance, a contact distance of i centimeters and a velocity of 10 meters per minute.

Tests which have been made show that the oxide coating ives the filament increased strength, and t is not onl reduces shrinkage which is `occasioned y shipping and otherwise moving the lamps from place to place before use, but also increases the life of the lamp during use. It is probable that the oxide coating acts to prevent the Wire from being injurlously affected, during flash aging and perhaps subsequently, by the chemicals, W ich are applied to the wire or put into the lamp such as phosphorus and getter materials.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. The method of treating tungsten. Wire for use as a filament in electric incandescent lamps and other electrical devices comprising filaments, which consists in coating the surface thereof with a thin film of metallic oxide and afterwards covering said film with a getter.

2. The method of treating tungsten wire for use as a filament in electric incandescent lamps and other electrical devices comprising filaments, which consists in oxidizing the surface thereot` and afterwards coating same with a getter.

rescate .having its surface coated with a thin film ofl metallic oxide and having said film covered with a getter containing phosphorus.

6. A filament for electric incandescent lamps and other electrical devices comprising filaments, consisting of tungsten having its surface coated with a thin film of tungstic oxide and having said film covered with a getter containing phosphorus.

In Witness whereof -I have hereunto set my hand this 27 day of July, 1922.

TED E. FOULKE. 

